Brown Recluse Spider in Iowa

Recent news coverage about the brown recluse spider in Iowa has sensationalized our situation and lead to unnecessary concern. We hope the following points help clarify the situation. Please also refer to ISU Extension pamphlet Pm-1721, "Potentially Dangerous Spiders."

  • The brown recluse spider is rare in Iowa. Less than 1 specimen per year is submitted to the Iowa Insect Diagnostic Clinic.
  • The brown recluse is a small spider with long spindly legs. The body is only about 3/8 inch long and tan to straw-brown.
  • The touted "violin-shaped marking" on the top of the cephalothorax varies in color and prominence. Several common spiders have dark markings on the cephalothorax that can be misconstrued as violin-shaped.
  • The brown recluse has only 6 eyes rather than the typical 8. The eyes are arranged in 3 pairs.
  • As the name implies, the brown recluse is reclusive. That is, they are secretive, rarely seen and difficult to find in their hiding places (cracks and gaps under and behind boxes, shelves, appliances and other items). Brown recluse spider are nocturnal.
  • Those rare brown recluse spiders found in Iowa are usually individual itinerants transported here from their normal range of the south central USA.
  • The brown recluse is found outdoors in the southern USA but in northern areas would only survive indoors.
  • The brown recluse is not aggressive. Bites are a defensive reaction used only when escape is not possible (such as when the spider is trapped against a person's skin).
  • Brown recluse spider bites are usually painless or accompanied by a slight stinging sensation. A localized burning sensation may last for an hour. Ulceration of the skin around a severe bite develops slowly but may persist for several weeks and require intensive medical attention.
  • Sanitation, especially vacuuming of harborages to remove spiders, webbing and egg sacs is the initial treatment technique. Insecticides are notoriously ineffective and should be limited to spot and void treatments of spider harborages.

This article originally appeared in the May 24, 2002 issue, p. 73.

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